Calibration of tiled projector systems with cameras and other optical sensors have become more and more commonplace. One of the main goals of an auto-calibration system is to maintain the quality of the system (such as linear geometry, uniform color and intensity) as the system ages, without the use of a trained technician. For example, it is desirable that a person with no training can push a “Calibrate’ button in a graphical user interface (GUI) and the system re-calibrates. It is not desirable that the user should be required to undertake a fine-tuning process requiring many interactions with a GUI, as that process can be time consuming and require training on the part of the user.
One tiled display that is particularly of interest is designed for use in a conference room environment. In a conference room, it is contemplated that a high resolution display can be constructed using M×N short throw projectors. When used in a front-projector configuration, short throw projectors are useful as one can walk right up to the screen without casting a shadow on the display until one is very close to the screen. Also, whether used in front projector or rear-projection setups, the projectors occupy a small depth which is useful in installations such as conference room, where there is limited space.
To calibrate such a system, it is often desirable to mount the camera very near the projectors. One reason this positioning is desirable is that it allows for a self-contained installation, which simplifies the task of the installer, and more generally lowers installation costs. This positioning is also desirable in that it avoids a condition in which a camera placed across a room space is more likely to be blocked by passers-by than a short throw arrangement. Locating such a camera across the room is also undesirable in that it typically requires cables to be run from the system to the camera, and that typically entails running such cables into the walls and around the room. This can be obtrusive and create an unaesthetic appearance in a public space. Alternatively it can prove time-consuming and costly to install the cables invisibly in the walls and/or ceiling.
Thus, a short throw camera is desirable in such installations as it allows for a self-contained installation and avoids undesirable wiring arrangements and blockage of the filed of view. However, when such a camera is close up to the display, at least two challenging effects occur. First, it can be necessary to employ a plurality of cameras with fish-eye, or other wide-angle, lenses because the cameras are not far from the screen, and it is otherwise difficult to image a significant field of view. Fish-eye lenses can be problematic because it can be difficult to accurately measure the distortions of the lenses. Furthermore, the distortion of the scene in the camera image is not only sensitive to the properties of the lens, but it is very sensitive to the positioning of the lens on top of the camera imager, and the position and orientation of the camera. The distortion is particularly sensitive toward the outside of the lenses. Thus, if one relies on the accuracy of the lens model of the fish-eye lenses during the projection display calibration, the resulting displayed images on the screen often appear distorted.
Also challenging is the fact that it can be prove challenging to image the entire screen with a short throw distance that can be only a few inches.
Thus, it is desirable to create an automatic calibration system that is straightforward to operate, does not rely on an accurate model of the camera distortion of the scene, and can handle situations where the camera cannot image the entire screen.